Chemodectoma in Dogs
Chemodectomas are generally benign tumors that grow from the chemoreceptor tissue of the body. These are the tissues that are most sensitive to chemical changes in the body, such as oxygen content and pH levels in the blood. While chemoreceptor tissues can be located throughout the body, chemodectomas mainly affect the chemoreceptor organs: the aorta and the carotid organs (i.e., heart and carotid artery).
Chemodectomas are relatively uncommon in dogs, but there does appear to be some breed and age predilection. Boxers and Boston Terriers, especially those over the age of ten, are most commonly affected. In addition, males tend to be more predisposed to aortic body tumors, while carotid body tumors show no gender predilection.
Symptoms and Types
Aortic body tumors occur on the aortic artery near the base of the heart. They are rarely of a malignant nature; they will grow within the space but not spread to the surrounding organs. These tumors become a health concern when their growth displaces the trachea, when they grow into the adjacent vessels, or when their growth places pressure on the atria or vena cava, impairing their functionality for conveying blood to the body and heart. Symptoms associated with aortic body tumors include:
- Trouble breathing
- Symptoms of right-sided congestive heart failure (CHF)
- Weakness, lethargy
Carotid body tumors, meanwhile, occur on the common carotid artery near the point of bifurcation -- where the artery splits into the internal and external carotid arteries. These arteries carry oxygenated blood to the head and neck, and are located in the neck. Because of this relation to the major arterial passages, carotid body tumors are often impossible to remove. In the majority of cases, these tumors remain slow growing but benign, and as with aortic tumors, they become a health issue when they invade the spaces of the adjacent blood vessels and lymphatic vessels. In an estimated 30 percent of cases, metastasis may occur into the surrounding organs, such as the lungs, bronchia or lymph nodes, or further into the liver or pancreas. Symptoms associated with carotid body tumors include:
Other symptoms seen in dogs affected by either body tumor type include:
- Severe hemorrhaging due to tumors in the blood vessels (can lead to sudden death)
- Metastasis to local blood vessels (up to 50 percent of cases )
- Organ failure due to cancerous growths (up to 20 percent of cases)
It is suspected that chronic lack of oxygen may be involved in chemodectoma development. This may explain why flat-faced (brachycephalic) breeds develop it more often. It is further suspected that environment my play a role in the growth of the tumor, as high altitudes may exacerbate lack of oxygen (hypoxemia) in disposed breeds.
After performing a thorough physical exam on your dog and taking a complete medical history from you, your veterinarian will order a chemical blood profile, complete blood count, urinalysis, and electrolyte panel. The results of these tests will give some indication of the whether the cancer has spread in the body. If hemorrhaging is occurring, anemia may be present, and if metastasis is taking place, higher than normal liver enzymes may be present in the bloodstream.
Chest X-rays will be used to identify the location of the mass and to check for cancer spread to the lungs or spine. A heart ultrasound will also be performed, and if heart impairment is suspected, an electrocardiogram (EKG) may be used to measure the heart’s ability to conduct electrical signals. If possible, a tissue sample will be taken from the mass for biopsy. This will provide a definite diagnosis.
Unfortunately, the prognosis for dogs with either of these types of tumors is grim. It is often very difficult to remove these tumors, and they will continue to grow until functioning of the surrounding vessels of organs is impaired to the point of cardiac arrest or organ failure. Cancer treating therapies, such as radiotherapy, can sometimes be used along with surgery to slow down the spread of these cancers.
Living and Management
Your dog will need to be re-evaluated by your veterinarian at least every three months for chest X-rays, as well as a physical exam to monitor for recurrence or spread of the cancer.